Ultra high frequency tank circuit



Jan. 3, 1939. J. w; CONKLJN 2,142,630

ULTRA HIGH FREQUENCY TANK CIRCUIT I Filed July 28, 1957 2 Sheets-Sheet l u fi //// lI/l/I Vl/l/ III! I! II l/l/ Zhmento:

Jan. 3, 1939. J. w. CONKLIN ULTRA HIGH FREQUENCY TANK CIRCUIT Filed July 28, 1957 2 Sheets-Sheet 2 RED (/1: 7/0

- inventor FE VEIPJHEZE 0707M attorney Patented Jan. 3, 1939 ULTRA HIGH FREQUENCY TANK CIRCUIT James W. Conklin, Audubon, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application July 28, 1937, Serial No. 156,114

4 Claims. (Cl. 178-44) My invention relates to ultra high frequency tank circuits in which means are provided for compensation of the expansion caused by the heating of elements of the circuit as the result of the currents flowing therein.

. It has been proposed to stabilize the frequency of ultra high frequency oscillatory currents by means of a quarter wave concentric line. While such resonant lines tend to stabilize high frequency currents flowing therein, it has been found that the heating effects of such currents expand the elements of the lines and thereby render the devices less stable. I am aware that several methods of temperature compensation have been mounted near the top of the hollow cylindrical member I. The spider may be reinforced by flanges ll. The spider includes at its center a hub l9, which is drilled to take the supporting shaft 2|. This shaft'is preferably made of a material which has very low coefficient of expansion, such as invar steel.

The top portion of the shaft is threaded, and mounted thereon is an adjustment nut 23. The shaft is prevented from turning during adjustment by a keyway 25 and a set screw 27. A tensioning spring 29 is positioned between the spider l5 and a retaining collar 3|, as shown. A conducting sleeve 33, surrounding the shaft 2| and l5 proposed but my experience has been that the Spring is Secured y a y u e means to ordinary temperature compensation which is the spider l5. A collar 35 locates the lower end suitable for fairly high frequency currents is not of the S1eeVe.33 With respect t e Shaft 2 l. sufficient for ultra high frequency oscillations. Oh the lower end of the Shaft 2| is Suitably By ultra high frequency oscillations is meant Cured metal disc The p e e ween t e 20 oscillatory currents of thirty megacycles and updisc 37 a d t e metal sleeve 33 includes an exrd pansion member 39, which is fastened to the It has also been customary to design such consleeve 33 and collar 35 at one end and to the disc centric resonant line stabilizers for a particular 37 at the other Ah inner metallifi Cylindrical frequency without providing means for adjustmember 4| is secured to the disc 31 by screws 43 ing the devices throughout a large range of freother Convenient fastening ea s- The eX- 25 quencies. My present invention contemplates, as an object, providing means whereby an ultra high frequency tank circuit may be arranged within a small space and may be adjusted over a large range of frequencies.

Another object of my invention is to provide an improved means for temperature compensation in an ultra high frequency resonant circuit.

Another object of my invention is to provide means for Vernier frequency adjustments from a point remote from the tank circuit.

An additional object is to provide a simple method of coupling, which may be adjusted for different frequencies.

My invention may be best understood by reference to the accompanying drawings in which Figure 1 is a sectional View of one embodiment of my invention,

Figure 2 is a plan view of the embodiment shown in Fig. 1, and

Figure 3 is a schematic diagram representing the circuit employed with my invention and means for making vernier adjustments.

Referring to Fig. 1, within an outer hollow cylindrical conductor member a pair of ports 3 and 5 are arranged to permit the insertion of coupling coils I, 9. At the lower end of the hollow cylindrical member is secured a metallic base member II, on which issuitably mounted a Vernier adjusting member l3. A metallic spider I5 is ternal diameter of the inner cylindrical member 4| is somewhat less than the internal diameter of the conductor member A number of lugs 45 are fastened to the upper portion of the metallic cylinder 4|; metallic rods 41 are secured 0 to the lugs 45. These rods project downwardly through the disc 37. The rods 4'! are preferably made of a metal having a very low coefiicient of expansion. A second metallic disc 49 is fastened to the lower ends of the rods 4'! so that the disc 35 49 is spaced from the disc 31. The space between the discs 31, 49 includes a metallic expansion member 5|, which is fastened to the two discs as shown. I

The Vernier I3 is comprised of an armature 40 which is mounted on a threaded adjusting screw 53. The adjusting screw may be coupled through a reducing gear to a reversible motor 51, as shown in Fig. 3. It should be understood that the reversing motor is not essential to the inven- 5 tion inasmuch as the Vernier l3 may be adjusted manually. A cover 59 may be mounted on the top of the cylinder member to house the spider l5 and the adjusting mechanism.

In order to cover a range of wave lengths with 50 one device, it should be understood that several different lengths of inner cylindrical members may be used. Each of said inner cylindrical members may be raised or lowered with respect to the base II to provide a course adjustment of 55 frequency, while the fine adjustment is obtained by the Vernier I3.

In the operation of these devices, the radio frequency currents passing through the tank circuit will generate heat, which causes the cylindrical members 33 and 4| to expand. While the two latter cylindrical members 33 and 4| expand, the effective length remains substantially constant because of the low coeflicient of expansion of the invar steel members 2| and 41. Any expansion of the members 33 and 4| does not change the effective length of these members, because such expansion is taken up by the expansion members 39 and 5|, respectively. The heating of the members 33 and 4| will cause an increase in their respective diameters. If the several members I, 33 and 4| are all made of the same material, the change in their diameters or radii will not change the ratio of the radii and, therefore, will not change the capacity between the several members. This statement may be made in View of the mathematical formula 1 I1 0 lO which is an expression of the capacity between inner and outer coaxial cylinders, where n equals the radius of the outer cylinder, r2 equals the radius of the inner cylinder, L equals the length of each cylinder, C equals the capacity in micromicrofarads, and k equals the dielectric constant.

It wil be observed that the outer conductor member is not provided with means for compensating for its expansion, while the inner cylindrical membe s are provided with temperature compensation means. It follows that as the member expands, the distance between the Vernier plate l3 and the disc 49 will increase. While this change in dimension could be prevented by tying the top and bottom of the member with a plurality of invar steel rods, I prefer to make use of this expansion characteristic. The effect of a change in length of the cylindrical member and hence of the capacity between the Vernier and the disc member 49, is to give the tank circuit a characteristic which will increase in frequency as the temperature increases This increasing temperature-frequency characteristic may be ofiset by other variations of frequency with temperature which go in the opposite direction. I have found that several elements of the circuit, other than the tank circuit per se, show a frequency characteristic which decreases with increasing temperature. By suitably adjusting the physical dimensions of the Vernier armature I3 and its space from the disc member 49, I have been able to obtain substantial cancellation of these opposing effects.

In Figs. 1, 2 and 3. similar reference numerals are used to indicate similar elements. In Fig. 2, the cover 59 has been omitted and the spider H5 is partly broken away to expose the inner cylindrical member All The coupling coil 1 is shown as mounted on an insulated member 6|.

In Fig. 3, pairs of tubes 65 and 6'! are shown connected in push-pull relation to the coupling coils and 9, respectively. It should be understood that a capacitive coupling or a combination of capacitive and inductive coupling may be used.

Thus, I have described an ultra high frequency tank circuit including means for compensating for temperature variations therein. I have also illustrated one form of coupling means applied to the said circuit, a course frequency adjusting means, and means for remotely controlling a vernier adjustment of the frequency of said circuit.

I claim as my invention:

1. An ultra high frequency concentric line resonator including an outer hollow cylindrical conducting member and an inner coaxial conducting sleeve, a metallic spider connecting said outer cylindrical member and said conducting sleeve at one of their adjacent ends; a metallic supporting shaft of low temperature coefficient of expansion located within and extending through said conducting sleeve and supported at one end by said metallic spider; a first metallic disc whose diameter is less than that of said outer cylindrical member but greater than that of said conducting sleeve coaxially connected to the free end of said supporting shaft; an inner metallic cylindrical member connected at its circumference to said metallic disc and enclosing a substantial portion of said conducting sleeve; a plurality of metallic rods of low temperature coeificient of expansion secured to the free end of said inner metallic cylindrical member, the axis of said rods being parallel to the axis of said inner cylindrical member, said rods extending beyond said metallic disc; a second metallic disc supported by said rods; and a metallic base member closing the free end of said outer hollow cylindrical conducting member and capacitively coupled to said second metallic disc.

2. In a device of the character of claim 1, means enabling longitudinal movement of said supporting shaft for adjusting the frequency of said circuit.

3. An ultra high frequency concentric line resonator including an outer hollow cylindrical conducting member and an inner coaxial conducting sleeve, a metallic spider connecting said outer cylindrical member and said conducting sleeve at one of their adjacent ends; a metallic supporting shaft of low temperature coefficient of expansion located within and extending through said conducting sleeve and supported at one end by said metallic spider; a first metallic disc whose diameter is less than that of said outer cylindrical member but greater than that of said conducting sleeve coaxially connected to the free end of said supporting shaft; a conductive metallic expansion member connecting said conducting sleeve and said first metallic disc; an inner metallic cylindrical member connected at its circumference to said metallic disc and enclosing a substantial portion of said conducting sleeve; a plurality of metallic rods of low temperature coefficient of expansion secured to the free end of said inner metallic cylindrical member, the axis of said rods being parallel to the axis of said inner cylindrical member, said rods extending beyond said metallic disc; a second metallic disc supported by said rods; a conductive metallic expansion member connecting said second metallic disc to said first metallic disc and said inner cylindrical member; and a metallic base member closing the free end of said outer hollow cylindrical conducting member and capacitively coupled to said second metallic disc.

4. A device of the character described in claim 3 which includes a small metallic disc parallel to said second metallic disc and movably mounted on said metallic base member for adjusting the frequency of said tuned circuit. 7

JAMES W. CONKLIN. 

